1. Field of the Invention
The present invention relates in general to an internal combustion engine, and more particularly to a fuel injection system of an internal combustion engine.
2. Description of Related Art
Several outboard motors recently have become equipped with fuel injection systems in response to increased concerns regarding hydrocarbon emissions. Such systems, which are monitored and controlled by an electronic control unit, significantly reduce hydrocarbon emissions, while improving fuel economy and performance.
Fuel injection system typically include a vapor separator and a high-pressure pump. The pump delivers pressurized fuel to the individual fuel injectors. An engine typically includes one, and sometimes two fuel injectors per cylinder. The pump must be of a sufficient size to supply fuel to the injectors at a desired pressure, while producing a significant flow rate through a fuel recirculation branch of the fuel delivery system to reduce the temperature of the fuel at the inlet to the fuel injector. Prior fuel delivery systems thus have included a large centrifugal type (e.g. Wesco-type) fuel pump in order to meet these needs.
Large-size pumps, however, generally increase the size of the engine, and thus the size of the power head. The power head of an outboard motor generally extends above the transom of the watercraft and, consequently, the power head produces aerodynamic drag on the watercraft as the watercraft speeds over the water. The size and shape of the power head directly affect the amount of drag produced. A large-size pump thus negatively increases the drag experienced by the outboard motor.
Many outboard motors which employ fuel injection system use an integrated vapor separator/fuel pump assembly. That is, a single housing encloses the fuel tank of the vapor separator and the fuel pump. The fuel pump draws fuel directly from the fuel tank. Although this design somewhat reduces the size of these components, the integrated design makes it difficult to service or repair the pump. A service technician must remove the entire housing and then disassemble the housing in order to gain access to the pump. This act commonly destroys the housing seal. The technician must then disconnect and remove the pump from the housing. After servicing, the technician reassembles the unit in the reverse manner, replacing the housing seal. These steps overly complicate the assembly and service procedures, and add cost to the service and maintenance of the outboard motor.
Another drawback of prior unitary vapor separator/fuel pump assemblies resides with the position of the pump inlet relative to the fuel tank of the vapor separator. Fuel vapor and air are separated from liquid fuel in the fuel tank of the vapor separator. The influent port to the fuel pump, which also commonly is located in the fuel tank, tends to draw in gas bubbles before the bubbles surface in the fuel tank of the vapor separator, especially where the pump influent port lies near the point where the fuel enters the tank through the supply inlet port. Vapor bubbles in the fuel line significantly alters the fuel ratio of the fuel/air charge delivered to the cylinder combustion chambers. Inefficiencies and rough running of the engine result from this effect. In addition, in some fuel delivery systems, the bubbles can produce a vapor-lock and prevent fuel flow through the high-pressure portion of the fuel delivery system.